The present invention relates to a fluidized-bed reaction apparatus with less pulverization of particles in a fluidized-bed reaction tower and less scattering of the particles therefrom and capable of easy temperature control, and a fluidizing bed reaction process using such an apparatus.
There has been the following problems in the treatment accompanying with the heat generation in a fluidized-bed in the fluidized-bed reaction tower.
In granulation and oxidative infusibilization of a petroleum pitch, for instance, it has been generally employed a process of subjecting a granulated pitch (pitch particles) to oxidative infusibilization treatment under the fluidized state thereof by air while elevating a temperature. However, since an excessive amount of air is required for removing large quantity of heat generated due to oxidation by using only the fluidizing air, even how the fluidized-bed is an apparatus excellent in view of the heat-utilizing efficiency because of the too low circulating speed of the particles, it can not be said preferable. Also, there is the similar problem in endothermic reaction. Further, although it may be considered to dispose a heat-removing device such as cooling pipes, etc. to the inside of the fluidized-bed, such a method is not preferable because the disposed pipes cause to hinder the fluidization of granulated particles thereby occurring local heat generation and uncontrollable exothermic reactions. Particularly, since a sufficient amount of oxidizing air for forming the fluidized-bed is supplied near a perforated plate as compared with other portions, as the size of the apparatus becomes large, if the movement of the particles slows down once, the amount of heat generated becomes greater than the amount of heat removed tending to cause rapid reaction. Generally, in order to make the movement of the particles vigorous the flow rate of the fluidizing gas should be raised, however, in a large scale apparatus, since the height of the fluidized-bed is increased in view of the processing efficiency, the fluidizing gas grows into huge gas bubbles and burst up in the upper portion of the fluidized-bed, thereby causing remarkable entrainment of the particles.
Further, the removal of heat by using cooling pipes, etc. does not show rapid response for the cooling effect substantially, making it difficult for the temperature control in the case of the exothermic reaction such as oxidation which is high in the temperature-dependency.
The present inventors have applied a method of water-spraying onto the fluidized-bed in the fluidized-bed reaction apparatus, in order to rapidly remove the heat of oxidation in the oxidative infusibilization reaction for granulated pitch, but it takes much time for the particles cooled in the upper portion to flow downwardly near the perforated plate in a large-scale fluidized-bed thus tending to form temperature distribution in the fluidized-bed. By such a reason, it causes such a vicious cycle that if a temperature distribution is once formed, a temperature is elevated more at a place where the temperature is higher.
Further, in conventional gas-solid type reaction apparatus, there has been employed a method of recovering pulverized and entrained particles by a cyclone and returning them to the inside of a fluidized-bed only for the purpose of reacting the fluidized particles with gases. As seen from such method, the improvement for the technique has usually been directed to increase the suerficial gas velocity but no substantial study has been made for the moderation of the movement of particles by lowering the superficial gas velocity as low as possible for obtaining products with no pulverized particles from the fluidized-bed.
The present inventors have studied on a process of fluidized-bed reaction and a fluidized-bed reaction apparatus capable of preventing the entrainment and pulverization of particles, increasing the circulation velocity of the particles and making temperature control easy, and as a result, it has been found that the circulation velocity of particles is great even if the average superficial gas velocity is low and the particles are scarcely pulverized or entrained, by using a fluidized-bed reaction apparatus comprising:
a perforated plate disposed in the lower portion of a fluidized-bed reaction tower for forming a fluidized-bed of particles thereon, having the opening ratio and the area each at a specific ratio between the outer peripheral portion and the inner portion, or between the outer peripheral portion with the geometrical central portion and the inner portion of the perforated plate,
an inlet of a heating-fluidizing gas located below the perforated plate,
an outlet of the particles located above the perforated plate,
an inlet of the particles receiving the reaction in the fluidized-bed, located in the upper portion of the reaction tower and above the fluidized-bed, and
an outlet of a discharge gas located at the top of the reaction tower; and
conducting the fluidized-bed reaction by introducing heating-fluidizing air at a temperature required for the reaction at a specific flow rate. Based on such findings, the present invention has been attained.